30/01/2012
CSI 2132 Tutorial 2
Conceptual Modeling:
The Entity-Relationship Model
Database Design: Overview
Get Requirements
and Data
Conceptual Model
Logical Model
Physical Model
2
1
30/01/2012
“Data Modeling Using ER”
Entity-Relationship Diagram

Entities
•
•

Entity Types and Entity Sets
Strong vs. Weak
Attributes
•
•
•
•

Key Attributes
Composite Attributes
Multi-valued Attributes
Derived Attributes
Relationships
•
•
•
•
Degree and cardinality
Role names
Partial vs. Total
Identifying relationships
3
“Data Modeling Using ER”
4
2
30/01/2012
“Data Modeling Using ER”
The ER diagram in the next slide shows
a simplified schema for an airline
reservations system.
Extract from the ER diagram the
requirements and constraints that
resulted in this schema. Be as precise
as possible.
5
Chapter 7: “Data Modeling Using ER”
6
3
30/01/2012
“Data Modeling Using ER”
The database represents each AIRPORT,
keeping its unique airport code, the airport
name and the city and state in which it is
located.
7
Chapter 7: “Data Modeling Using ER”
Each airline FLIGHT has a unique number,
the airline to which it belongs and the
weekdays on which it is scheduled.
8
4
30/01/2012
Chapter 7: “Data Modeling Using ER”
Each airline FLIGHT has a unique number,
the airline to which it belongs and the
weekdays on which it is scheduled.
9
“Data Modeling Using ER”
A flight is composed of one or more
FLIGHT LEGS. Each FLIGHT LEG has a
departure airport and scheduled departure
time and an arrival airport and scheduled
10
arrival time.
5
30/01/2012
Chapter 7: “Data Modeling Using ER”
11
“Data Modeling Using ER”
A LEG INSTANCE is an instance of a
FLIGHT LEG on a specific date (for
example, AC1223 leg 1 on July 30, 2011).
The actual departure and arrival airports
and times are recorded for each flight leg
after it concludes. The number of available
seats and the airplane used in the LEG
INSTANCE are also kept.
12
6
30/01/2012
“Data Modeling Using ER”
The customer RESERVATION on each leg
instance includes the customer name,
phone and seat number(s) for each
reservation.
13
“Data Modeling Using ER”
Information on
AIRPLANEs and
AIRPLANE TYPEs
are also kept.
For each airplane
type (e.g. DC-10),
the type name,
manufacturing
company, and
maximum number
of seats are kept.
14
7
30/01/2012
“Data Modeling Using ER”
The airports in
which planes of
this type can land
are kept in the
database.
For each airplane,
its ID, total
number of seats
and type are
recorded.
15
“Data Modeling Using ER”
A database is needed to keep track of
the teams and games of a sports
league. A team has a number of players,
not all of whom participate in each
game.
The players participating in each game
for each team are recorded, as well as
the positions they played in that game,
and the result of the game.
16
8
30/01/2012
“Data Modeling Using ER”
Try to design an ER schema diagram for
this application, clearly stating any
assumptions you make.
Choose your favorite sport (hockey,
soccer, football, baseball ...)
17
“Data Modeling Using ER”
Assumptions:
•
Each game in the schedule is
univocally identified by a number
and the combination of date, starting
time and field.
•
The performance of an individual
player in a game keeps the
information needed for statistics and
may be quite complex.
18
9
30/01/2012
Chapter 7: “Data Modeling Using ER”
19
“Data Modeling Using ER”
Consider a CONFERENCE_REVIEW
database in which researchers submit
their papers for consideration. Referee
reviews are recorded for use in the
paper selection process.
The DB system caters primarily to
reviewers who record answers to
evaluation questions for each paper
they review and make
recommendations regarding rejection
or acceptance.
20
10
30/01/2012
“Data Modeling Using ER”
•
Paper authors are uniquely identified
by their email address. First and last
names are also recorded.
•
Each paper gets a unique ID and is
described by a title, abstract and the
digital file containing the paper.
•
A paper may have multiple authors.
One of them is designated as the
contact author.
21
“Data Modeling Using ER”
•
Paper reviewers are univocally
identified by their email addresses.
Each reviewer’s first name, last
name, phone number, affiliation and
topics of interest are also recorded.
•
Each paper is assigned between two
and four reviewers. A reviewer rates
each paper assigned on 1-10 scale in
four categories: technical merit,
readability, originality and relevance
to the conference. An overall
recommendation is finally provided. 22
11
30/01/2012
“Data Modeling Using ER”
•
Each review contains two types of
written comments: one to be seen by
the review committee and the other
as feedback to the author(s).
Design an ER diagram for the
CONFERENCE REVIEW database.
23
Chapter 7: “Data Modeling Using ER”
24
12
30/01/2012
CSI 2132 Tutorial 2
Conceptual Modeling:
The Entity-Relationship Model
13